The use of cellulose (chromatography paper) as a cheap, versatile and
non-covalent support for organic molecules during multi-step synthesis
Stephen E. Shanahan, Douglas D. Byrne, Graham G. A. Inglis, Mahbub Alam and Simon J. F.
Macdonald*
Medicinal Chemistry 1, ri CEDD, GlaxoSmithKline Medicines Research Centre, Gunnels Wood Rd,
Stevenage, UK SG1 2NY. E-mail: simon.jf.macdonald@gsk.com; Fax: 44 (0)1438 763615
Received (in Cambridge, UK) 20th August 2002, Accepted 17th September 2002
First published as an Advance Article on the web 3rd October 2002
Cellulose chromatography paper provides a novel non-
covalent support for synthesis and in-situ purification of
multi-dimensional arrays.
of the reaction were conducted on different tiles; tiles could then
be sacrificed for analysis at intermediate points by extraction
with boiling ethyl acetate and the resulting solutions analysed
by LC/MS.† In this manner, formation of impure amide 2 was
observed by LC/MS.
The recent use of support technologies for the production of
libraries and focussed arrays of compounds for biological
evaluation has become commonplace and features a wide range
of chemistries.1 Primarily, these technologies rely upon the
covalent attachment of the substrate to a matrix. Many different
types of matrices have been used, from three-dimensional
supports such as polystyrene beads1 to planar supports such as
glass2 and cellulose sheets.3 Many of these sophisticated
supports are expensive, present specific handling issues and can
require elaborate techniques for the attachment of the substrate,
for the derivation of the support surface prior to attachment and
for deconvolution. Often only very small quantities (sub-
milligram) of the final products are produced.
An important component of this system is the ability to
remove unreacted starting materials from the tile by washing
with acidic or basic aqueous solutions. Un-ionised organic
substrates tend to remain associated with the paper when it is
washed with aqueous solutions and conversely, ionisable
organic substrates or inorganic water soluble salts are removed
by exposure to an aqueous environment. This forms the basis of
an in-situ purification method for impure reaction products
absorbed on the support. Amide 2 was purified by washing the
support briefly with both aqueous base (to remove unreacted
benzoyl chloride) and aqueous acid (to remove excess amine 1).
The support was then dried by irradiating in a microwave oven.
Amide 2 remained non-covalently associated with the cellulose
Recently, Williams4 has described the use of thin layer
chromatography for reaction optimisation of a piperazine array.
This is the only instance of which we are aware, where the
substrate is not covalently attached to a support which might be
used for the production of arrays. We describe here the use of
cellulose (Whatman 17CHR Chromatography Paper) as a very
cheap and versatile support where the substrates are not
covalently attached but instead simply absorbed onto the
cellulose. This stands in contrast to previous reports where the
substrate is covalently attached to derivatised cellulose.3
Importantly, even when the substrates are only absorbed on the
support, sequential chemical transformations are still feasible.
The compounds can be purified whilst still absorbed on the
support and the final products can be prepared in milligram
quantities. In addition, the format provides significant advan-
tages in handling and in reaction monitoring over conventional
supports where the substrates are covalently bound.
1
paper in good purity, as observed by LC/MS and H-NMR
analysis of material extracted from a sacrificial tile.
Conversion of 2 to carboxylic acid 3 was achieved by
subsequent brief treatment of the dried support with neat
trifluoroacetic acid. This led to slight swelling of the support
(increasing with time) but no observed leaching of substrate.
Following drying under a nitrogen stream, final extraction gave
3 in high purity by LC/MS and 1H-NMR (68% yield from 1).
A 3 3 5 array of 15 N-substituted amino acids was prepared
using the cellulose support technology in order to test the
generality of the method and to determine ease of handling
when synthesising multiple samples (Table 1). Chemistry
(Scheme 2) was analogous to the previous two step preparation
of 3 from tert-butyl glycinate 1, and utilised similar scale and
experimental procedures. Included were reactions of amines
with acid chlorides, sulfonyl chlorides and chloroformates.‡
Each sequence was conducted on a separate tile. Whilst the
yields (over two steps) of final products obtained varied from
moderate to good, the purities were generally excellent,§
indicating the efficiency of the washing procedures.
All the chemistry described here was carried out on 10 3 10
3 0.9 mm square shaped pieces (a ‘tile’) of the cellulose
chromatography paper, cut from the commercially available
sheets using scissors.
Substrates and reagents can be loaded onto the paper simply
by application as neat liquids or solutions with a Gilson pipette.
Loading the reagent mixture as a single application to the centre
of a cellulose square was found to give complete and even
distribution.
Further work investigated a three step reaction sequence
using the cellulose support technology (Scheme 3). Using
protocols analogous to those already described, bis-amide 8 was
isolated in 33% overall yield. This result demonstrates that the
Experimental techniques were optimised for a model reaction
sequence conducted on 0.04 mmol scale, where typically 6mg
of substrate are loaded onto a tile in 40 ml of liquid. (Scheme
1).
Benzoyl chloride was first loaded neat onto the cellulose
support. tert-Butyl glycinate 1 was then pre-mixed with an
excess of triethylamine and similarly loaded. Although 1 was an
oil, it was found that pre-mixing it with triethylamine simplified
the loading procedure by reducing its viscosity. Multiple repeats
Scheme 1
Scheme 2
2554
CHEM. COMMUN., 2002, 2554–2555
This journal is © The Royal Society of Chemistry 2002
Shanahan, Stephen E.
